Powerpoint help, please!?

I am creating a jeopardy game for my Government cl using Powerpoint 2007. However, i would like to make it so that once you click on one of the ons that links to a question, the on changes-has a strike-through or is gray or something of the sort, so that i know it has already been clicked once i link back to my main page. i do NOT want to make multiple main page slides with different ones struck through-that would take too long. can anyone help me?